1. Technical Field
This invention relates to a heat exchanger for a refrigeration circuit and more particularly, to an evaporator for an automotive air conditioning refrigeration circuit.
2. Description of the Prior Art
Evaporators for use in automotive air conditioning refrigeration circuits are known in the art, for example, U.S. Pat. No. 4,892,143 to Ishii. With reference to FIG. 1, a serpentine-type evaporator or heat exchanger discussed in the Ishii '143 patent is shown. Evaporator 100 includes a continuous serpentine tube 101 through which refrigeration fluid flows. Serpentine tube 101 includes a plurality of spaced, planar portions 101a and a corresponding plurality of curved connecting portions 101b. The planar portions 101a are parallel to one another and vertically disposed so as to be parallel to the flow direction "A" of air which passes an exterior surface of evaporator 100. One end of serpentine tube 101 is brazed to a fluid inlet pipe 102. The fluid inlet pipe 102 is linked to the output of a compression or an expansion means (for example, a compressor, not shown) of a refrigeration circuit. The other end of serpentine tube 101 is brazed to a fluid outlet pipe 103. The fluid outlet pipe 103 is linked to the inlet of the compressor.
Refrigeration fluid is provided to serpentine tube 101 from the compressor via inlet pipe 102, flows through each successive planar portion 101a and connecting portion 101b towards outlet pipe 103, and is then returned to the compressor. Of course, the refrigeration circuit may include other elements disposed between the compressor and evaporator 100.
The curved connecting portions of the evaporator discussed in Ishii '143 are formed by bending a straight tube. However, when the number of planar portions of the evaporator are increased in order to increase its ability to exchange heat, the radius of curvature of the curved connecting portions must be decreased. When a straight tube is bent with a small radius, the outer region of the resulting curved connecting portion becomes excessively thin. As a result, the mechanical strength and corrosion resistance of the outer regions is remarkably decreased. Therefore, the life of the evaporator decreases considerably. Accordingly, the ability of the Ishii device to exchange heat can only be increased a small amount due to the limits on the number of planar portions which can be formed.
Furthermore, since the refrigeration fluid flows through each of the planar portions and the curved connecting portions in succession from the inlet pipe to the outlet pipe, the efficiency of the heat exchange between the refrigeration fluid flowing through the serpentine tube and the air passing the exterior surface of the evaporator gradually decreases from the inlet pipe to the outlet pipe. Therefore, the air temperature leaving the exterior surface of the evaporator is not uniform across the evaporator. As a result, an improved elaborate automobile air conditioning system cannot be obtained.
Moreover, the water drops condensed on the exterior surface of the evaporator tend to be concentrated at an inner surface of each of the lower curved connecting portions. These gathered water drops may be scattered into the passenger compartment of an automobile by the air blown from an evaporator fan.